The present disclosure relates generally to satellite communications, and more specifically to systems and methods for dynamic antenna platform offset calibration.
An Earth-based antenna terminal for communication with a satellite typically has high antenna gain and a narrow beam pointed at the satellite, because of the large distance to the satellite and to avoid interference with other satellites. Mobile terminals on mobile vehicles may include an antenna system having a positioner to maintain pointing (or tracking) of the beam of the antenna system at the satellite during movement of the mobile vehicle.
Pointing error (e.g., misalignment) between a direction of maximum gain of the beam of the antenna and the actual direction from the antenna to the satellite can have a detrimental effect on the quality of the communication link between the antenna and the satellite. Relatively small misalignment may be compensated for by reducing a modulation and coding rate of signals communicated between the antenna system and the satellite. However, to maintain a given data rate (e.g., bits-per-second (bps)), this approach may increase system resource usage and thus result in inefficient use of the resources. Pointing error can also be associated with challenges in ensuring compliance with interference requirements with other satellites that are imposed by regulatory agencies (e.g., Federal Communications Commission (FCC), International Telecommunication Union (ITU), etc.) and/or a coordination agreement with operators of the other satellites.
Pointing error associated with an antenna system mounted to a mobile vehicle may result from misalignment between a sensor (e.g., an inertial reference unit (IRU)) of the mobile vehicle and the antenna system (e.g., a mounting platform of the antenna system), which may be referred to as antenna platform misalignment. Antenna platform misalignment may be caused by manufacturing tolerances between the sensor and the antenna system, structural deflections caused by movement and other disturbances, and other factors. In order to compensate for pointing error, whether associated with antenna platform misalignment or other factors, the mobile antenna terminal may perform a signal-based mispointing correction operation such as peaking, conical scan, sine scan, and similar methods. However, mispointing correction operations may not properly correct for antenna platform misalignment in all beam directions. Further, the mispointing correction operations may require a dedicated calibration routine that inhibits user communications, and may require the mobile vehicle to be pointed in orientations associated with the calibration routine.